SE1551633A1

SE1551633A1 - Impulse wrench rotation detection

Info

Publication number: SE1551633A1
Application number: SE1551633A
Authority: SE
Inventors: Robert Christian Friberg John
Original assignee: Atlas Copco Ind Technique Ab
Priority date: 2015-12-14
Filing date: 2015-12-14
Publication date: 2017-04-11
Also published as: KR20180089423A; CN108367416A; CN108367416B; US20180354107A1; EP3389928A1; JP2019502566A; EP3389928B1; SE539112C2; US10668603B2; KR102571847B1; JP6812438B2; WO2017102585A1

Abstract

P20-15716-151211 13 Abstract. A method for detecting deviations between the angulardisplacement actually obtained in a screw joint being tightenedby an impulse type power wrench and the angular displacementdetermined via angle measurements between the impulse unit (l2)of the power wrench and the power wrench housing (lO), whereinthe angular interval (Aël) between the end points (AE, BE) of afirst delivered impulse (A) and a succeeding second deliveredimpulse (B) is compared with the angular interval (Aëz) betweenthe start points (BS, CS) of a second and a succeeding thirddelivered impulse (B,C), whereby occurring angular displacementsof the power wrench housing (lO) during impulse delivery aredetectable as a difference between these two angular intervals (AQ1 and Aëﬂ. (Fig. 3)

Description

P20-15716-151211 Impulse wrench rotation detection.

Technical field The invention relates a method and a device for detectingoccurring deviations between the rotational movement actuallyobtained in a screw joint being tightened by an impulse typepower wrench and the angular displacements of and the angulardisplacement measured between the power wrench housing and the impulse unit of the power wrench.

Background Because of the dynamic characteristics of the delivered shortlasting torque impulses there is a problem to measure theactually delivered output torque magnitude in this type of powerwrenches. Due to varying frictional resistance in screw jointsthe torque level is not a definite measurement of the actuallyobtained clamping force anyway. So, instead of trying todetermine the torque imposed on the screw joint the morereliable clamping force is determined by measuring andestablishing the sum of the rotational increments imposed onscrew joint by repeated torque impulses. In consideration of thepre-established angle-to-clamping-force relationship of theactual screw joint, i.e. the pitch of the screw joint thread,the sum of the rotational increments corresponds to a certainclamping force obtained in screw joint. Accordingly, the totalrotational movement of the output shaft is obtained bysummarizing the rotational increments can be indicated by an angle encoder provided at the impulse unit of the power wrench.

In practice this has been done by measuring the rotationalincrements of the inertia drive member of the impulse unit inrelation to the power wrench housing and forming a sum of theseincrements. However, this gives a correct information of the amount of rotation imposed on the screw joint being tightened P20-15716-151211 only if the power wrench housing remains absolutely immobileduring the tightening operation. If however some rotationaldisplacement of the power wrench housing occurs the anglemeasurement in the power wrench impulse unit would be misleadingand not correspond to the actually obtained rotational movementof the screw joint. This means that the sum of the rotationalincrements measured in the impulse unit gives misleadinginformation of the tightening level actually obtained in the screw joint.

So, there is a problem to verify the true amount of rotationimposed on the screw joint, because manually supported tools ofthis type are dependent on the operator's ability to keep thewrench housing immobile during torque delivery. In some casesthe impulse wrench may tend to rotate somewhat in the oppositedirection due to reaction forces transferred to the wrenchhousing during torque delivery. In other cases the operator,consciously or not, may rotate the wrench housing in thetightening direction which also makes the rotational incrementsindicated by the angle encoder of the wrench misleading as tothe actual rotational movement imposed on the screw joint being tightened.

This means that in cases where the operator does not succeed tokeep the power wrench housing immobile, i.e. to preventrotational displacements of the housing during tightening, thedata obtained from the angle encoder of the impulse mechanismwill not give a true information on the obtained screw joint rotation and, hence, the tightening level of a screw joint.

Summary It is an object of the invention to provide a method forestablishing whether the rotational movement actually imposed ona screw joint during tightening by a manually supported impulse type power wrench corresponds to the sum of rotational P20-15716-151211 increments of the output shaft of the wrench indicated by an angle encoder provided at the impulse unit of the wrench.

It is a further object of the invention to provide a method toestablish whether the rotational movement actually imposed on ascrew joint during tightening by a manually supported impulsetype power wrench corresponds to the sum of rotationalincrements of the output shaft of the wrench indicated at theimpulse unit by comparing angular displacements of the impulseunit relative to the wrench housing at delivery of succeeding impulses.

These object or some other objects are obtained by the method and device as set out in the appended claims.

The invention aims to detect deviations between the rotationalmovement actually imposed on a screw joint being tightened andthe angular displacements measured on the impulse generatingunit of the power wrench to thereby detect occurring rotationaldisplacements of the power wrench housing during a screw jointtightening operation. In particular, the invention enablesstudying and analyzing the individual movements of the torqueimpulse generating unit of an impulse wrench during operation tothereby verify the tightening result accomplished by thedelivered torque impulses. The individual movements can bestudied and analyzed to determine deviations without the use of a gyro.

In accordance with one embodiment a method for detectingdeviations between the angular displacement actually obtained ina screw joint being tightened by an impulse type power wrenchand the angular displacement measured between the power wrenchhousing and the impulse unit of the power wrench is provided.The method comprises to determine a first angular intervalbetween an end point of a first delivered impulse and an endpoint of a succeeding second delivered impulse, and to determining a second angular interval between a start point of P20-15716-151211 said second delivered impulse and a start point of a succeedingthird delivered impulse. The first angular interval is comparedto the second angular interval to determine the differencebetween the first and the second angular intervals. A deviationis then determined to exist between the angular displacementactually obtained in a screw joint being tightened by an impulsetype power wrench and the angular displacement measured betweenthe power wrench housing and the impulse unit of the powerwrench based on the determined difference between said first andsaid second angular intervals Aël and AQZ. Hence a deviation ofthe measured angular rotation and the actual angular rotation ofa screw, nut or bolt caused by a rotational movement of thepower wrench during tightening of a joint can be detected bydetecting a difference between the first and second angularintervals. These measurements can be recorded without the use ofany additional sensors such as a gyro, and the detection cantherefore be implemented without any significant additional costs.

In accordance with one embodiment the end and start points ofthe succeeding delivered torque impulses are chosen as certainrotation speed change levels of the impulse unit of the power wrench.

In accordance with one embodiment the determination that adeviation exists is based on a comparison between the determineddifference between said first and said second angular intervals and a pre-set threshold value.

In accordance with one embodiment output of an alert signal isgenerated when a deviation is determined to exist between the first and the second angular intervals, respectively.

The invention also extends to a computer program productcomprising instructions for implementing the method and todifferent devices that can utilize the method such as a power wrench or a control unit connected to and controlling a power P20-15716-151211 wrench. Still further objects and advantages of the invention will appear from the following specification and claims.

Brief description of drawings The invention will now be described in further detail in thefollowing specification and claims with reference to the accompanying drawings, in which.

- Fig. l shows schematically a side view, partly in section, ofan impulse type power wrench illustrating the impulse generatingunit with an angle encoder, - Fig. 2 shows a diagram illustrating the angular speed overtime of the inertia drive member of the power wrench impulsegenerating unit in relation to the power wrench housing, and - Fig. 3 is a flow chart illustrating some procedural steps performed when detecting an angular deviation.

Detailed description The method according to the invention is intended to be appliedon an impulse type power wrench having a manually supportedhousing lO with a rotation motor and an impulse generating unitl2. The latter comprises an inertia drive member l3 coupled to amotor and arranged to transfer kinetic energy intermittently toan anvil member connected to the output shaft l4 of the,typically hand held, power wrench. The energy transfer isaccomplished via a hydraulic medium confined in the impulsegenerating unit. Since the impulse generating unit is of acommon well known type and design a further detailed description thereof is left out of this specification.

The impulse generating unit also comprises an angle sensor suchas an angle encoder l6 for indicating and measuring therotational movements of the inertia drive member l3 of the impulse unit l2 in relation to the housing lO during each P20-15716-151211 generated torque impulse to thereby enable measurement of therotational displacements of the output shaft 14 and, hence, thestepwise angular displacements of a screw joint being tightened.The sum of these angular displacements corresponds to theclamping force obtained in the screw joint. This is easilycalculated in view of the thread pitch of the screw joint. Theangle encoder 16 in accordance with the embodiment shown in Fig.1 is of a prior art type and comprises a circumferential band 17mounted on the inertia drive member 13 and having a large numberof magnetized transverse stripes. Other angle sensors can beused in other embodiments. A sensor 18 is secured in the housing10 and being activated by the magnetized stripes of the band 17 at rotation of the inertial drive member 13.

The rotation speed/time diagram of Fig. 2 illustrates parts ofthree succeeding torque impulses wherein start points as well asend points of these impulses are indicated. To the left in thediagram an end point AE of a first impulse A is chosen as acertain degree of rotation speed increase of the inertia drivemember in relation to the housing. The following impulse B ispreceded by an acceleration phase X of the inertia drive member,and the start point BE of the impulse B is chosen as a decreaseof the inertia drive member rotation speed. The impulse B iscompleted at an end point BEand is succeeded by a third impulseC which is preceded by an acceleration phase Y. The Impulse C begins at a start point CE Each one of the points AE, AE, BE, BE and CE, CE represents anangular position of the inertia drive member 13 relation to thehousing 10, which means that it is possible to determine anangular interval Aël between the end point AE of impulse A andthe end point BE of impulse B as well as an angular interval Aëzbetween the start point BE of impulse B and the start point CE of impulse C.

If the power wrench housing during impulse delivery has been kept completely immobile during generation of the torque P20-15716-151211 impulses A, B and C the angular intervals Aël and Aëg should beidentical. Accordingly, if an angular displacement of the powerwrench housing has occurred during the impulse delivery adifference between the angular intervals AQ1 and AQ2 can beobserved. Such a difference in angular displacement indicatesthat a movement of the power wench housing has occurred and thatthe measured and calculated sum of the angular displacements ofthe inertia drive member does not truly correspond to theangular displacement actually imposed on the screw joint beingtightened. This means that the accomplished clamping force ortightening level of the screw joint does not truly correspond tothe indicated and calculated sum of angular displacements of theinertia drive member of the impulse unit and that the tighteninglevel actually obtained should be checked for ascertaining thequality and safety of the screw joint. In accordance with someembodiments an indicator such as a light or sound generatingdevice is provided on the power wrench or in the vicinity of theoperator operating the power wrench to indicate that screw joint should be checked.

In Fig. 3 a flow chart illustration some procedural steps thatcan be performed by a computer program when performing themethod as set out herein. First in a step 301 a first angularinterval Aël between an end point AE of a first deliveredimpulse A and an end point BE of a succeeding second delivered impulse B is determined.

Next, in a step 303 a second angular interval A@2 between astart point BS of said second delivered impulse B and a startpoint CS of a succeeding third delivered impulse C isdetermined. Thereupon, in a step 305 the first angular intervalAël is compared with the second angular interval A@2) todetermine the difference between said first and said secondangular intervals (AQ1 and AQ2). An occurring difference betweensaid first and said second angular intervals (A@l and A@2) indicates a deviation between the angular displacement measured P20-15716-151211 between the power wrench housing (10) and the impulse unit (12)and the angular displacement actually imposed on the screw jointbeing tightened. If a difference is determined to exist betweenthe first and the second angular intervals A@1 and A@2,respectively in a step 305, a deviation between the angulardisplacement measured between the power wrench housing 10 andthe impulse unit 12 and the angular displacement actuallyimposed on the screw joint being tightened is determined toexist in a step 307. A signal alerting the operator or a controlsystem can then be output to make the operator of the powerwrench aware of a potentially inferior screw joint in a step 309.

In accordance with one exemplary embodiment a difference isdetermined to exist in step 307 if the difference exceeds a pre-set threshold value. The pre-set threshold value can be setdifferently for different screw joint to compensate for different tolerances acceptable for different screw joints.

In accordance with some embodiments, data relating to adetermined potentially inferior screw joint can also be loggedfor follow-up purposes and to form a basis for statisticsregarding a particular power wrench or a particular operator todetermine if a problem exists with a particular power wrench ora particular operator. This can for example be determined bycomparing a frequency at which a potentially inferior screwjoint is determine with some predetermined value(s). The datathat is logged can for example comprise one or more of: time,identity of power wrench, identity of operator, and magnitude of the determined difference.

By the methods and devices according to the invention it ispossible to detect uncertainties of the delivered tighteningmovements imposed on a screw joint being tightened and, hencethe finally obtained tightening level of the screw joint,without adding any extra equipment in the form of for instance gyros to the power wrench. Occurring angular displacements of P20-15716-151211 the power wrench housing during impulse delivery may be detectedby an angle sensor such an angle encoder in the impulse unit which is standard equipment in most impulse wrenches today.

The method can be implemented using suitable software executedon a computer. The software can be stored on a non-volatiledevice. In accordance with some embodiment the power wrench it-self houses the hardware such as a central processor unit and anassociated memory that comprises the software enabling theexecution of the method as described herein. In accordance withsome other embodiments the method is executed in a power tool controller located remote from the power wrench.

Claims

P20-15716-151211 Claims

1. l. A method for detecting deviations between the angulardisplacement actually obtained in a screw joint being tightenedby an impulse type power wrench and the angular displacementmeasured between the power wrench housing (l0) and the impulseunit (l2) of the power wrench, c h a r a c t e r i z e d by the following steps: 0 determining (30l) a first angular interval (Aël) between anend point (AE) of a first delivered impulse (A) and an endpoint (BE) of a succeeding second delivered impulse (B), 0 determining (303) a second angular interval (AQ2) between astart point (BS) of said second delivered impulse (B) and astart point (CS) of a succeeding third delivered impulse(C), 0 comparing (305) said first angular interval (Aël) with saidsecond angular interval (Aëg) , to determine the differencebetween said first and said second angular intervals (A@1and Aëz), and 0 determining (307) that a deviation exists between theangular displacement actually obtained in a screw jointbeing tightened by an impulse type power wrench and theangular displacement measured between the power wrenchhousing (l0) and the impulse unit (l2) of the power wrenchbased on the determined difference between said first and said second angular intervals (Aël and Aëﬂ.

2. Method according to claim l, wherein said end and startpoints (AE, BE and BS, CS) of the succeeding delivered torqueimpulses (A, B, C) are chosen as certain rotation speed change levels of the impulse unit of the power wrench.

3. Method according to claim l or 2, wherein the determination that a deviation exists is based on a comparison between the P20-15716-151211 11 determined difference between said first and said second angular intervals (Aël and AQ2) and a pre-set threshold value.

4. Method according to anyone of claims l - 3, furthercomprising output (309) of an alert signal when a deviation isdetermined to exist between the first and the second angular intervals Aël and A@2, respectively.

5. A computer program product comprising a non-transitorycomputer readable medium storing computer instructions fordetecting deviations between the angular displacement actuallyobtained in a screw joint being tightened by an impulse typepower wrench and the angular displacement measured between thepower wrench housing (l0) and the impulse unit (l2) of the powerwrench, computer program product comprising instructions thatwhen executed on a computer causes the computer to perform thefollowing steps: 0 determining (30l) a first angular interval (Aël) between anend point (AE) of a first delivered impulse (A) and an endpoint (BE) of a succeeding second delivered impulse (B), 0 determining (303) a second angular interval (AQ2) between astart point (BS) of said second delivered impulse (B) and astart point (CS) of a succeeding third delivered impulse(C), 0 comparing (305) said first angular interval (AQ1) with saidsecond angular interval (Aëg) , to determine the differencebetween said first and said second angular intervals (A@1and Aëz), and 0 determining (307) that a deviation exists between thefirst and the second angular intervals A@l and A@2,respectively based on the determined difference between said first and said second angular intervals (A@1 and Aëﬂ.

6. A device for detecting deviations between the angular displacement actually obtained in a screw joint being tightened P20-15716-151211 12 by an impulse type power wrench and the angular displacement measured between the power wrench housing unit (10) and the impulse (12) of the power wrench, c h a r a c t e r i z e d by: a determination circuit adapted to determine a first (Aëi) (AE) first delivered impulse (BE) angular interval between an end point of a (A) and an end point of a succeeding second delivered impulse (B),a determination circuit adapted to determine a second (Aëz) (Bs) second delivered impulse (CQ angular interval between a start point of said (B) and a start point of a succeeding third delivered impulse (C),a comparator adapted to compare said first angular(ÅÉ1) (ÅÖ2) 1 determine the difference between said first and said (Aël and A@ﬂ, interval with said second angular interval to second angular intervals and determination circuit adapted to determine that adeviation exists between the first and the second angularintervals Aël and A@2, respectively based on thedetermined difference between said first and said second angular intervals (AQ1 and Agﬂ.

7. A power wrench comprising the device according to claim 6.

8. A power wrench controller unit comprising the device according to claim 6.